Bookmaking requires the use of a wide variety of adhesives. Adhesives are used in making hard book covers, casing book blocks into hard covers, applying paper covers to book blocks, and the binding of book blocks themselves. The binding of book blocks themselves is generally the most demanding adhesive application in the industry. Adhesives may be used alone or in cooperation with other mechanical binders such as sewing and staples.
One use of adhesives in binding book blocks is as a primer to wet the spine area of the book block and provide a tie coat for an additional adhesive layer. The additional adhesive layer provides structural support and generally maintains the mechanical integrity of the binding. Priming adhesives are generally aqueous emulsions of film-forming polymers which can readily wet the spine of the book block. The emulsions may be thermoplastic copolymers, acrylates, animal glues, etc. An example of a particular primer composition is disclosed in Hume, III, U.S. Pat. No. 4,536,012. This reference discloses a significant advance in the art and employs a latex primer composition which includes ungelatinized starch particles to form a primer film resistant to blistering and subsequent charring. The latex primer composition is generally prepared from such known resins as vinyl acetate-acrylic acid copolymers, styrene-butadiene copolymers, and ethylene-vinyl acetate (EVA) copolymers, etc.
Structural adhesives may be either aqueous emulsions or hot melt adhesives. The aqueous emulsions are primarily EVA's, polyvinylacetates (PVAc's), or other vinyl copolymers which incorporate external plasticizers. Hot melts are often thermoplastic styrene block copolymers or EVA's. An example of a particular hot melt structural adhesive composition is disclosed in Malcolm et al., U.S. Pat. No. 5,090,861. This reference also discloses a significant advance in the art and relates to the use of radial block copolymer, a tackifying resin, and a plasticizing oil in a hot melt adhesive for bookbinding. This adhesive has enhanced resistance to cold flow and creep.
There are a number of methods of binding book blocks during book manufacture. These methods employ mechanical fasteners (e.g., sewn or stapled bindings), mechanical fasteners in conjunction with adhesives, or purely adhesive bindings. Generally, high quality books are prepared form signatures (bundles of pages) which are sewn together. These signatures are then combined with adhesives to form the binding. However, this process is generally limited to books which require a very structurally sound binding.
One of the most widely used binding methods today is known as perfect binding. This may be used for either hard or soft cover bindings. In perfect binding, the sewing of signatures is eliminated. The pages are printed on a web of paper, and the book block is formed by folding this web and arranging into a signature stack. One or more signatures are then clamped and cut, and the page folds are cut and roughened or otherwise prepared for the application of the binding adhesives. The adhesives essentially provide all of the structural support for the book's binding. This requires the adhesives formulator to carefully balance such properties as strength, flexibility, resistance to cold flow, resistance to low temperature embrittlement, etc. The balancing of strength and flexibility has been particularly difficult.
In hard cover or case bookbinding, an important structural form of the binding is called the rounding of the spine or binding. This is the convex shape of the spine which distributes the stresses of opening the book across the width of the binding. It is important that a binding maintain its rounding in high quality books to provide stress distribution for the life of the book. Many current adhesives are incapable of providing years of maintaining the rounding. A new development in rounding is disclosed in Carter et al., U.S. Pat. No. 4,907,822. This reference relates to the use of a polyurethane hot melt adhesive to bind book block signatures and rounding the bound book blocks. However, there are limitations and difficulties in applying polyurethane hot melts, e.g. (1) lack of green strength (3-7 day cure), (2) requires use of special equipment, and (3) presents toxicity and requires increased ventilation issues due to the presence of free isocyanate. Therefore, bookbinders are constantly demanding improvements in this area.
A recent innovation in the bookbinding industry relates to the creation of paperback books having some of the attributes of hard bound books. This is being introduced as the OTABIND.TM. system, and is discussed in Rebsamen, "OTABIND--A New Lay-flat Paperback Binding", Publishers Weekly, pp. 83-88 (Mar. 4, 1988), and Jukola, U.S. Pat. No. 4,299,410 and G.B. Pat. No. 2100670B. This binding system incorporates two separate emulsion adhesives to bind the book blocks. The binding allows the manufacture of soft cover books having the ability to be opened flat without breaking the binding as normally occurs with low cost, mass produced paperbacks using hot melt adhesives. This system also produces books having improved cold temperature performance. While the OTABIND.TM. process may be an improvement in technique, there remains a need for improved aqueous adhesives for use in the system.
The bookbinding industry continues to demand increased performance from adhesives manufacturers. In particular, improvements are required in drying characteristics, bond strength, flexibility, shape retention, and versatility of aqueous emulsion bookbinding adhesives. Therefore, a new and versatile aqueous emulsion bookbinding adhesive is needed which can be used as a primer by itself to provide permanent rounding and shape retention, excellent bond strength, and acceptable drying characteristics.